In recent years requirements for the quality of steel materials have become stricter and stricter, and the need to save energy and to economize on labor has increased. Thus, continuous casting now accounts for a large proportion of the steel production, and in connection with this trend, the monitoring and control of molten steel has become far more important. In the monitoring of molten steel, one of the most important factors is the activity of oxygen in molten steel. And it is well known that success in the measurement thereof has a great influence upon the subsequent steelmaking process.
Accordingly, the oxygen probe which determines the activity of oxygen in molten steel by means of the electromotive force of a concentration cell has been developed and is commercially available.
Although the known oxygen probe is protected with a high quality refractory material, the allowable immersion time is limited when it is directly dipped in molten steel. Therefore, in order to determine oxygen activity correctly it is necessary for an oxygen probe that its electromotive force (hereinafter simply referred to as "emf") be stabilized within the allowable immersion time, and that the stabilized state be maintained without disruption for a period of time. Also it must exhibit good reproducibility in order to secure the determined values with reliability.
However, the known oxygen probes have a disadvantage in that they must be immersed for a long time before the caused emf is stabilized, or the emf fluctuates after the response time has passed, that is, they are inadequate in response and stability. Also they are not satisfactory in reproducibility either, and therefore they are not yet practically used in production lines in steelmaking plants.
Therefore, there has been a demand for an improved oxygen probe which has improved response, stability and reproducibility and thus is satisfactory for use in actual production lines.
However, we do not know of any report which discusses and analyzes the above-mentioned defects of the conventional oxygen probes, and suggests measures for improvement thereof. We have noted that the factor which has the most important influence on response, stability and reproducibility is the reference electrode, and tried to improve the reference electrode and completed this invention.